1. Field of the Invention
This invention relates to a bearing steel, more particularly, to a steel suitable for the material of bearings to be used at a high temperature.
2. State of the Art
Bearings supporting a main rotating shaft of a gas turbine are used under very severe conditions of a high temperature in addition to a very high peripheral speed.
Needless to say, a heat engine exhibits a higher efficiency when it is operated at a higher temperature, and therefore, it is desired to raise the operation temperature of a turbine up to the allowable limit. The bearings are also requested to have a heat resistance durable at a temperature of 300.degree. C. or more. Further, as the results of higher speed and larger size, the peripheral velocity of the bearings becomes inevitably higher. Bearings are required to have high reliability to secure safety operation of rotational machinery for a long period of time.
The representative heat resistant bearing steel presently being used is AISI-M50 steel, which consists of 0.77-0.85% C, up to 0.35% Si, up to 0.35% Mn, 3.75-4.25% Cr, 4.00-4.50% Mo and 0.90-1.10% V, and the balance being Fe and inevitable impurities.
It is demanded to give higher reliability under severe working conditions to this material or other steels of similar alloy compositions.